Our main project deals with understanding the organization of the unique grid-like network of skeletal muscle fiber microtubules. Results obtained in previous years by Sarah Oddoux, Kristien Zaal and others using fluorescent protein constructs expressed in muscle fibers ex vivo and in vivo showed that this microtubule network, apparently static, is in fact composed of highly dynamic microtubules moving along each other. We also used the technique of fluorescence recovery after photobleaching (FRAP) to investigate the mechanism of microtubule movement. Our results supported microtubule growth, rather than transport, as the main mechanism. In the past year we have consolidated this work for publication. The manuscript has just been accepted for publication, while two other manuscripts have been favorably reviewed and are undergoing revisions. We have started a new series of experiments aimed at understanding how microtubules in the mdx mouse, the mouse model for DMD, differ from the microtubules in wild-type mice. This is interesting because mdx muscle fibers have an abnormal microtubule network, and microtubules play a role in the mdx pathology. Our initial results suggest that microtubule nucleation and growth in mdx fibers differ in several respects from the regrowth in normal fibers. This work will be continued during this calendar year. The second project we have consolidated for publication deals with Wenhua Liu's new quantitation method for evaluating directionality of a line pattern such as an image of microtubules. Muscle microtubules form a complex network and visual assessment can be tricky. The new algorithm will be helpful for unbiased observation of changes in microtubule patterns. Using this tool we have re-evaluated images of microtubules in 3-week old vs. 12 week-old mdx mice. The already mentioned mdx mice have abnormal microtubules. If this abnormality is directly linked to the absence of dystrophin, it should be manifest at a young age, before the first wave of muscle fiber regeneration. From a visual examination of microtubules that is what we concluded and published (Prins et al., 2009). However, a recent report (Khairallah et al., 2012) suggests that only older mice show microtubule defects. We have repeated the image analysis from 3-week-old vs. 12-week-old mice, using the new software instead of visual examination. The results confirmed and qualified our initial assessment (manuscript currently being revised).